SOLVED -- scrollbar not work in Windows7

My app uses CJ controls, including DockingPane and SkinFramework.
One user had my app working OK in WindowsXP, but when he installed on Windows7 he reports that vertical scrollbar does not work. (Looks OK on screen but does not respond to mouse).

Other users with Windows7 have not got this problem.

I sent user a test program with same core functions but NOT using CJ Docking or Skin. This has scrollbar working OK in Windows7.

I guess there is something different about his new computer that causes vertical scrollbar not to work with CJ controls.

Can you suggest anything to try?
Any idea what could cause this?

SOLVED -- changing to a diifferent visual theme and scrollbar works OK.

Thanks for the suggestion.  It seems it must be something that works OK in WindowsXP but not on this particular Windows7 PC (but OK on other Windows7 PCs).

I guess from the lack of replies that nobody else has encountered this problem (which is a useful answer in itself :-)

chrisABC wrote: It seems it is a visual theme that is causing the problem. If user selects different theme, scrollbar works OK. Thanks for the suggestion